Ecological Risks from Atmospheric Deposition of Nitrogen and Sulphur in Jack Pine forests of Northwestern Canada

Chronic elevated nitrogen (N) deposition can have adverse effects on terrestrial ecosystems. For large areas of northern Canada distant from emissions sources, long-range atmospheric transport N may impact plant species diversity, even at low levels. The objective this study was to establish community thresholds for under multiple environmental gradients using gradient forest analysis. Plant abundance data 297 Jack pine (Pinus banksiana Lamb.)-dominant plots across Alberta and Saskatchewan, Canada, were evaluated against 43 bioclimatic variables. Bioclimatic variables overwhelmingly the most important drivers thresholds. Nonetheless, dry oxide (DNO) dioxide inferred a total deposited (TDN) threshold 1.4–2.1 kg ha?1 yr?1. This range predominantly associated with changes in several lichen species, including Cladina mitis, Vulpicida pinastri, Evernia mesomorpha Lecanora circumborealis, some which are known bioindicators deposition. A secondary DNO appeared be driving vascular equivalent 2.45–3.15 yr?1 TDN gradient. These results suggest that ‘background’ regions biodiversity-based empirical critical load 1.4–3.15 will protect communities other N-sensitive forests Northwestern Canada. Nitrogen above lead biodiversity within these forests.